Dynamic tissue holding device with low profile spring

ABSTRACT

A dynamic tissue holding device is disclosed for dynamically holding two tissue portions in contact with one another. The device comprises a biasing spring having a relatively low profile, and a band adapted for extending about the tissue portions to be held together. The band has a first end for attachment to a first attachment portion on the biasing spring and a second end for attachment to a second attachment portion on the biasing spring. The band establishes a path of tension along its length and extending linearly between the two ends of the band. Advantageously, more than one-half of the biasing spring is disposed outside of the path of tension when the dynamic tissue holding device is in place and holding the two tissue portions together.

This application claims the benefit under 35 U.S.C. 119(e) of the filingdate of Provisional U.S. Application Ser. No. 61/037,582, entitledDynamic Ring Compression Device, filed on Mar. 18, 2008, and expresslyincorporated herein by reference, in its entirety. This application isalso related to co-pending U.S. patent application Ser. No. 12/347,821,entitled Dynamic Suture Tensioning Device and filed on Dec. 31, 2008,and to U.S. Utility Patent Application Docket Nos. A-2313, entitledKnotless Dynamic Suture Tensioning Device and Methods, and A-2396,entitled Load Shaping for Dynamic Tensioning Mechanisms and Methods,both filed on even date herewith, all of which are commonly assigned andexpressly incorporated herein, by reference, in their entirety.

BACKGROUND OF THE INVENTION

The present invention is related to the general surgical repair ofseparated body tissues, and more particularly to internally fixating andstabilizing such body tissues, specifically bones.

In the present state of the art, there are a number of systems availableto repair biological tissues separated in surgery or by injury. Theseproducts serve to approximate and stabilize the tissues so that healingmay commence and provide compression in the interface to promotehealing. Compression and stability are critical for proper anatomicalhealing of tissue. With the correct amount of compression applied to theinterface of the tissue portions to be joined, signals are sent to thetissue, thus allowing the tissue to remodel in proper anatomicalposition. The amount of compression applied to the tissue interfaceneeds to be appropriate to the type of tissue that is being healed.

When it is necessary to access the thoracic cavity for a medicalprocedure, for example, it is required to cut the sternum into twopieces using a rib spreader. Once the procedure is completed within thethoracic cavity, the sternum must be repaired. For such repairs, it isknown to use a dynamic compression device like that shown in FIGS. 1(device 14) and 2, which, for the sake of convenience and clarity, isdiscussed in connection with the discussion of the inventive device 12,in the detailed description portion of the specification. Some of thedrawbacks of this typical device 14, and others which are used include:

1. Bulky spring materials, while occupying substantial space, often donot store much energy. Some use polymer elastic bands, while other usecoiled springs;

2. Wires are sometimes used to wrap the bones into position incompression with one another. However, wires can have sharp ends thatcan damage adjunctive tissues. Knot stacks in suture can interfere withthe natural movement of surrounding tissues; and

3. Current banding systems that incorporate a biasing mechanism toachieve dynamic compression, like the device 14 described hereinbelow,put the biasing mechanism in line with the band or suture. This practicecompetes with precious space at the healing site. Suture or bands areused to approximate tissues so that they may heal. It is desirable toobtain the best purchase possible on the tissue, so that the bindingmechanics offered by the suture may be utilized. The best purchase isoptimized by ensuring that the suture has the greatest contact area withthe tissue. If a biasing mechanism is interfering with this concept, thebiasing mechanism may diminish the suture's ability to hold the tissuestogether.

What is needed is an improved dynamic compression system which addressesand overcomes these shortcomings in an innovative way.

SUMMARY OF THE INVENTION

The present invention solves the problems outlined above by providing abiasing system for a suture or banding system that does not adverselyaffect the band's ability to hold tissue together. This is done byremoving most or all of the biasing mechanism from the path of the band.By placing the biasing mechanism to one or the other side of the tensionpath of the band, many desirable effects are realized.

The inventor has recognized that maximizing contact between the sutureor band and the underlying bone or tissue is important to optimizehealing. This is particularly relevant in the case of holding sternalhalves together after they have been separated to access the thoraciccavity. Breathing, coughing, and any movement by the upper body impartlarger forces in the repair held together by bands. Any biasing devicemust serve to augment or maintain the function of the bands. If this isnot the case, coughing may induce stresses that concentrate on one partof the bone, causing the bands to cut into the bone. When the bands cutinto the bone, the tension in the bands is released adversely, thusaffecting their ability to help mend bone to bone.

More particularly, there is provided in one aspect of the invention adynamic tissue holding device for dynamically holding two tissueportions in contact with one another. The device comprises a biasingspring having a relatively low profile, and a band adapted for extendingabout the tissue portions to be held together. The band has a first endfor attachment to a first attachment portion on the biasing spring and asecond end for attachment to a second attachment portion on the biasingspring. The band establishes a path of tension along its length andextending linearly between the two ends of the band. Advantageously,more than one-half of the biasing spring is disposed outside of the pathof tension when the dynamic tissue holding device is in place andholding the two tissue portions together.

Advantageously, at least approximately four-fifths of the biasing springis disposed outside of the path of tension. The height of the biasingspring is less than about 2 mm. In one particular embodiment, thebiasing spring is formed to have a generally parabolic profile. The bandpreferably comprises a braided band, or, alternatively, a cable.

In one embodiment of the invention, the biasing spring comprises a firsteyelet disposed in a center portion of the spring, for receiving thefirst end of the tensioning band, and a second eyelet disposed on anopposing side of the center portion of the spring, for receiving thesecond end of the tensioning band, wherein at least approximatelyfour-fifths of the spring is disposed on either one side or the other ofthe first and second eyelets. More preferably, approximately two-fifthsof the spring is disposed on one side of the first and second eyeletsand approximately two-fifths of the spring is disposed on the other sideof the first and second eyelets. The space efficiency of the biasingspring is at least about 50%, and preferably at least about 57%.

In another embodiment of the invention, the biasing spring comprises afirst eyelet disposed on one edge of the spring, for receiving the firstend of the tensioning band, and a second eyelet disposed on a secondedge of the spring, for receiving the second end of the tensioning band,wherein substantially all of the biasing spring is disposed to one sideof said eyelets.

In another aspect of the invention, there is provided a dynamic tissueholding device for dynamically holding two tissue portions in contactwith one another, which comprises a biasing spring and a band adaptedfor extending about the tissue portions to be held together. The bandhas a first end for attachment to a first attachment portion on thebiasing spring and a second end for attachment to a second attachmentportion on the biasing spring. A particularly advantageous feature ofthe invention is that the aspect ratio of the inventive device, definedas the height of the device above the tissue surface, divided by thelength of the device, is less than or equal to approximately 0.50, andmore preferably approximately 0.10.

The height of the biasing spring is less than about 2 mm. In oneparticular embodiment, the biasing spring is formed to have a generallyparabolic profile. The band preferably comprises a braided band, or,alternatively, a cable.

In one embodiment of the invention, the biasing spring comprises a firsteyelet disposed in a center portion of the spring, for receiving thefirst end of the tensioning band, and a second eyelet disposed on anopposing side of the center portion of the spring, for receiving thesecond end of the tensioning band, wherein at least approximatelyfour-fifths of the spring is disposed on either one side or the other ofthe first and second eyelets. More preferably, approximately two-fifthsof the spring is disposed on one side of the first and second eyeletsand approximately two-fifths of the spring is disposed on the other sideof the first and second eyelets. The space efficiency of the biasingspring is at least about 50%, and preferably at least about 57%.

In another embodiment of the invention, the biasing spring comprises afirst eyelet disposed on one edge of the spring, for receiving the firstend of the tensioning band, and a second eyelet disposed on a secondedge of the spring, for receiving the second end of the tensioning band,wherein substantially all of the biasing spring is disposed to one sideof said eyelets.

The invention, together with additional features and advantages thereof,may best be understood by reference to the following description takenin conjunction with the accompanying illustrative drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an isometric view showing a sternum having bone halves whichare being held together by a device constructed in accordance with theprinciples of the present invention, and also by a prior art device, forcomparative purposes;

FIG. 2 is a top cross-sectional view of the prior art dynamiccompression device shown in FIG. 1;

FIG. 3 is a top cross-sectional view similar to FIG. 2 of the dynamiccompression device of the present invention also shown in FIG. 1;

FIG. 4 is a cross-sectional view of the sternum shown in FIG. 1,illustrating the respective profiles of each of the prior art device andthe inventive device;

FIG. 5 is an isometric view of a coiled spring for use as a drawbarspring in the prior art device of FIG. 2;

FIG. 6 is an isometric view similar to FIG. 5 of the prior art coiledspring in a compressed configuration;

FIG. 7 is an isometric view of the device of the present invention in acompressed configuration;

FIG. 8 is an isometric view similar to FIG. 7 of the device in anexpanded configuration;

FIG. 9 is an isometric view of an alternative embodiment of theinvention, in its initial relaxed state; and

FIG. 10 is an isometric view similar to FIG. 9, illustrating thealternative embodiment is its tensioned, energy stored state.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now more particularly to the drawings, there is shown in FIG.1 a sternum 10 which is comprised of two bone halves 16 and 18. The twobone halves have been separated, as is necessary for performance of openheart surgical procedures, or other procedures requiring access to thethoracic cavity. To conclude the procedure, it is necessary to re-jointhe bone halves 16 and 18 and to do so in a way that will ensure properhealing.

A dynamic compression device 12, which has been constructed inaccordance with the principles of the present invention, is illustratedin a deployed orientation for holding the bone halves 16, 18 together.Also illustrated is a typical prior art dynamic compression device 14,also in a deployed configuration, for purposes of comparison. Withreference also to FIG. 2, the prior art device 14 uses a biasingmechanism-suture configuration, wherein the biasing mechanism comprisesa drawbar spring 26 which is placed directly in line with the tension ofa length of suture 22. The biasing mechanism 26 serves to pull the bonehalves 16 and 18 into each other by means of tensioning suture 22, thusholding the sternum 10 together so that it may heal.

Now referring to FIG. 3, as well as FIG. 1, the inventive device 12functions to pull the upper intercostal spaces together by means of abraided band 20 and a biasing spring 24. The braided band 20 mayalternative comprise a cable and still be well within the scope of thepresent invention. The entirety of the drawbar spring element 26 ofdevice 14 can be seen to be directly in the path of the tension ofsuture 22. On the other hand, in the present invention 12, four-fifthsof the flat biasing spring 24 lies outside of the tension path of theband 20. This feature offers several significant advantages over theprior art approach.

FIGS. 2 and 3, taken side-by-side, as well as FIG. 4, clearlydemonstrate the advantageous features of the inventive device 12,respective to the typical prior art device 14. FIG. 2 is a topcross-sectional view of the prior art device 14, as situated on apatient's sternum 10, and FIG. 3 is a similar cross-sectional viewshowing the inventive device 12 similarly situated on the patient'ssternum. FIG. 4 is a cross-sectional view, perpendicular to theosteotomy showing bone half 16, and extending through the sternum anddevices 12 and 14 (see FIG. 1). In this view, the profile of theinventive device 12 can be easily compared to that of the prior artdevice 14. The aspect ratio may be used as a measurement of the profile.The aspect ratio of device 12 is defined as the height 31 of the deviceabove the bony surface, divided by the length 33 of the device. In theillustrated embodiment of device 12, its aspect ratio is approximately1/10. Other suitable inventive devices may have aspect ratios of up toabout ½ and still realize substantial benefits of the present invention.In contrast, the prior art drawbar spring device 14 has an aspect ratioof its height 27 divided by its length 29, which is approximately 1.

Both of the devices 12 and 14 are constructed of a suitable knownmedical grade material, preferably surgical stainless steel, to therebyyield similar performance characteristics which are necessary to supplydynamic compression to sternal halves 16, 18 so that optimum healing mayoccur. Sternal halves 16, 18 also represent a typical sternalcross-section in its width of approximately 24 mm.

The width of the sternum 10 ends up being a critical dimension in theprocedure. The width of an adult sternum may range from 18 to 80 mm, butthe tissue may not be dissected to access its entire width. Whiledissection may be done to accommodate larger devices, such trauma totissue should be avoided. Thus, the figures show a sternal width ofapproximately 24 mm as this is the common dissected width used toaccommodate the saw used for the initial osteomety.

At 24 mm in sternal width, the prior art device 14 is too large tofunction correctly. The suture 22 is unable to wrap around the boneappropriately, causing gaps 42 and 44. The gaps 42 and 44 cause thesuture 22 to pull the device 14 directly into the sternal halves 16 and18. This causes a rise in suture tension to realize the same compressionbetween sternal halves 16 and 18, should gaps 42 and 44 not be present.The tension is such, in the system of device 14, that it is likely thatarms 38 and 40 of the device will bend to the point of affecting thereturning function of the spring 26. The net effect is that the device14 cannot supply the same compression between the sternal halves 16 and18 as is the case with the inventive device 12, even though the springs26 and 24, respectively, have substantially the same spring constantsand are fabricated of the same material. The width 29 of the prior artdevice 14 is twice the width 33 of the inventive device 12. Theinventive device 12 also shows smaller gaps, with the band 20 lying onthe bone surfaces 34, 36, enabling the band 20 to hold tension on bothsides of the bone.

The dermal layer on top of the sternum is rather thin. Even when asurgeon employs only twisted wire to repair the sternum, some patientscan feel that wire under their skin. Consequently, the profile of aclosure device can have cosmetic as well as practical concerns. Thedermal layer over the sternum on an average adult female is 5 to 10 mmthick. The prior art device 14 has a height 27 of approximately 5.3 mm(FIG. 4). This is sufficiently thick to be rather clearly seen in someadults. As noted above, the device 14 presents a much higher profile offthe sternum 10 (the difference in profile between the two devices beingshown as reference numeral 32) than does the inventive device 12, whichhas only a height 31 (FIG. 4) of about 1.8 mm off the sternum. Moreover,because the profile of the inventive device 12 is spread out over alarge surface area, resulting in a much more favorable aspect ratio, itwill not be easily seen when viewing the patient from the outside.

FIGS. 5 and 6 illustrate the drawbar 26 of the prior art device 14 ingreater detail. FIG. 5 illustrates the coiled spring 52 in its initial,untensioned configuration. An eyelet 54 is connected to the arm 38,which moves freely through an end cap 50 and is solidly attached to anend cap 48. And eyelet 56 is connected to the arm 40, which moves freelythrough the end cap 48 and is solidly attached to the end cap 50. Thespring 52 is trapped between the end caps 50 and 48. As the eyelets 54and 56 are drawn apart, as is needed to tension the suture, end caps 50and 48 are drawn together, thus compressing the spring 52 and causingthe spring 52 to store energy as shown in FIG. 6.

FIG. 1 clearly shows the width requirement for the device on the topsurface of the sternum, and FIGS. 2 and 4 show the deficiencies of thedrawbar spring design. FIG. 5 illustrates how the drawbar spring isinherently a poor design. As can be seen in FIG. 5, the eyelets 54 and56 are necessarily placed outside of the ends of spring end caps 48 and50. It is because of the way that the drawbar design is assembled thatthis must be so. Eyelets 54 and 56 are then pulled farther apart tofully compress the spring 52.

The space efficiency of the device 12 is an important design criteria. Asmaller, more efficient spring enables the device 12 to be used in morescenarios with less trauma to the patient. A material is capable ofstoring energy based on its volume. How that energy is stored andreleased is based on the length of the material and its cross-section.Both devices 12 and 14 have been designed to have equivalent performanceboth in energy stored and in the delivery of the energy. However, therespective space efficiencies of the springs of each device are fardifferent. The space efficiency of the spring is defined as the totalspace it occupies divided by the space or volume the spring materialactually physically occupies. In the case of the prior art device 14,the spring wire is 0.040 in. in diameter, and makes 7.5 revolutions. Thespring itself is 0.210 in. in diameter and is 0.475 in. long. Thus, thespace efficiency of the device 14 is the volume of the spring wiredivided by the volume occupied by the spring, which equals 32%. Notethat the end caps 50 and 48, and the arms 38 and 40 are left out of thiscalculation because they do not store energy. There is also some designspace beneath the spring, between the bone and the spring that is notused and could be used by other designs. With this space included, thespace efficiency of the device 14 drops to 28%.

The inventive device 12 more than doubles this space efficiency at 57%,by following a few innovative precepts. As can be seen in FIG. 7, theinventive device more closely spaces the eyelets 60 and 62, therebyeliminating the dead space in the width of the design. The springcross-section is rectangular, thus eliminating the wasted space broughton by a wire. The spring starts in its most compacted state, widthwise,so that spaces between the spring elements do not contribute to thewidth of the device.

Advantageously, the spring 24 as shown particularly in FIGS. 7 and 8 isfabricated from a flat sheet of material. Grooves 68 are made as smallas possible, using the smallest cutter possible. A presently preferredcutting method is by a Wire Electrical Discharge Machine (wire EDM),because it can accurately cut the parabolic profile of the springs whichis necessary for an optimum spring performance. However, alternativecutting approaches may utilize laser, plasma cutters, band saws, waterjets, photo etching, etc., wherein the cutting process enables a highdensity of biasing elements, and wherein the cutting process achievessuch a high density by cutting the left side of one element and theright side of another element using the same cut. Cutting these slotsusing just one pass of the machine also shortens machining time, whichlowers the cost of the device.

FIG. 8 illustrates the spring 24 in its expanded state, storing all ofthe energy needed to force the tissues under the suture in compressionthroughout the healing cycle. Preferably, approximately ⅘ of the springis disposed above the eyelets at 64 and below the eyelets at 66. Thisenables the width of the device to be as small as possible.

FIGS. 9 and 10 illustrate another embodiment of the present invention,wherein the entire spring element 76 is paced to one side of sutureeyelets 72 and 74. FIG. 9 shows the spring element in its initialrelaxed state, and FIG. 10 shows the embodiment in its tensioned, energystored state.

While the inventive concept is disclosed as being particularly adaptedfor use in repairing the sternum after a thoracic cavity procedure, itis, of course, applicable to a great many other procedures requiringrepair of bodily tissue, particularly bone.

Accordingly, although exemplary embodiments of the invention have beenshown and described, it is to be understood that all the terms usedherein are descriptive rather than limiting, and that many changes,modifications, and substitutions may be made by one having ordinaryskill in the art without departing from the spirit and scope of theinvention, which is to be limited only in accordance with the followingclaims.

1. A dynamic tissue holding device for dynamically holding two tissueportions in contact with one another, the device comprising: a biasingspring having a relatively low profile and comprising a substantiallyflat material; and a band adapted for extending about the tissueportions to be held together, the band having a first end attached to afirst attachment portion on the biasing spring and the band extending ina direction from the first end away from the spring, and a second endattached to a second attachment portion on the biasing spring and theband extending in a direction from the second end away from the spring;the band establishing a path of tension along its length and extendinglinearly between the two ends of the band, in a configuration so thatthe band and the spring together form a loop, with the spring forming apart of the length of the loop; said biasing spring comprising a firsteyelet disposed in a center portion of the spring, for receiving thefirst end of the tensioning band, and a second eyelet disposed on anopposing side of the center portion of the spring, for receiving thesecond end of the tensioning band, wherein at least approximatelyfour-fifths of the spring is disposed on either one side or the other ofthe first and second eyelets; wherein more than one-half of the biasingspring is disposed outside of said path of tension when the dynamictissue holding device is in place and holding the two tissue portionstogether.
 2. The dynamic tissue holding device as recited in claim 1,wherein at least approximately four-fifths of the biasing spring isdisposed outside of said path of tension.
 3. The dynamic tissue holdingdevice as recited in claim 1, wherein the height of said biasing springis less than 2 mm.
 4. The dynamic tissue holding device as recited inclaim 1, wherein the biasing spring is formed to have a generallyparabolic profile.
 5. The dynamic tissue holding device as recited inclaim 1, wherein the band comprises a braided band.
 6. The dynamictissue holding device as recited in claim 1, wherein the band comprisesa cable.
 7. (canceled)
 8. The dynamic tissue holding device as recitedin claim 1, wherein approximately two-fifths of the spring is disposedon one side of the first and second eyelets and approximately two-fifthsof the spring is disposed on the other side of the first and secondeyelets.
 9. The dynamic tissue holding device as recited in claim 1,wherein the space efficiency of the biasing spring is at least or about50%.
 10. The dynamic tissue holding device as recited in claim 1,wherein the space efficiency of the biasing spring is at least or about57%.
 11. (canceled)
 12. The dynamic tissue holding device as recited inclaim 1, wherein the aspect ratio of the device is less than or equal toapproximately 0.50.
 13. The dynamic tissue holding device as recited inclaim 12, wherein the aspect ratio of the device is approximately 0.10.14. A dynamic tissue holding device for dynamically holding two tissueportions in contact with one another, the device comprising: a biasingspring comprised of a substantially flat material; and a band adaptedfor extending about the tissue portions to be held together, the bandhaving a first end attached to a first attachment portion on the biasingspring and the band extending in a direction from the first end awayfrom the spring, and a second end attached to a second attachmentportion on the biasing spring and the band extending in a direction fromthe second end away from the spring; the band establishing a path oftension along its length and extending linearly between the two ends ofthe band, in a configuration so that the band and the spring togetherform a loop, with the spring forming a part of the length of the loop;wherein said biasing spring comprises a first eyelet disposed in acenter portion of the spring, for receiving the first end of thetensioning band, and a second eyelet disposed on an opposing side of thecenter portion of the spring, for receiving the second end of thetensioning band, wherein at least approximately four-fifths of thespring is disposed on either one side or the other of the first andsecond eyelets; and further wherein the aspect ratio of the device isless than or equal to approximately 0.50.
 15. The dynamic tissue holdingdevice as recited in claim 14, wherein the aspect ratio of the device isapproximately 0.10.
 16. The dynamic tissue holding device as recited inclaim 14, wherein the biasing spring is formed to have a generallyparabolic profile.
 17. The dynamic tissue holding device as recited inclaim 14, wherein the height of said biasing spring is less than about 2mm.
 18. (canceled)
 19. The dynamic tissue holding device as recited inClaim 14, wherein approximately two-fifths of the spring is disposed onone side of the first and second eyelets and approximately two-fifths ofthe spring is disposed on the other side of the first and secondeyelets.
 20. The dynamic tissue holding device as recited in claim 14,wherein the space efficiency of the biasing spring is at least about50%.
 21. (canceled)